When it has been desirable or necessary to remove gas bubbles from liquids flowing in closed systems, the art has employed devices known as bubble traps. One such need for a bubble trap has been removal of air bubbles from blood flowing extracorporeally through a dialyzer. A leak in the system where it is under negative pressure may cause such air bubble formation.
One method of bubble removal used in some bubble traps is to let the momentum of upflowing liquid carry the bubbles to the surface where they are expelled. The outlet is positioned away from the liquid surface to receive debubbled liquid.
It would also be desirable to slow down the flow of liquid toward the outlet and thereby reduce the drag of the liquid on the entrapped bubbles that do not immediately reach the surface so that such bubbles will be more likely to reach the surface by their own buoyancy. One way to slow down the flow is to increase the area of the flow passage toward the outlet.
Another desirable feature for a bubble trap is an ability to be connected in-line into a system (i.e., the trap can simply replace a section of the fluid line, without the need for alterations in the plumbing, including introducing bends in the lines with the possibility of kinks under negative pressure).
Finally, a bubble trap that could serve the added purpose of monitoring blood pressure would be desirable, particularly if it were not necessary actually to introduce blood into the pressure monitoring circuit.
Serfass et al. U.S. Pat. No. 3,827,561 shows a dialysate head vessel having a submerged riser of smaller diameter than that of the vessel itself and an outlet apparently coming out the vessel bottom. Bubbles rise with inlet flow, but no way is shown for an in-line connection of the vessel. In Galletti et al., Heart-Lung Bypass--Principles and Techniques of Extracorporeal Circulation (1962, Grune and Stratton), the device shown in FIG. 53A (p. 156) operates in an initially upflow mode, but, if anything, there is a decrease in flow passage area as the blood cascades toward the outlet, and the device is not connected in-line, for the inlet and outlet are at right angles. Finally, Collins U.S. Pat. No. 3,295,297 shows a device that is closer to having an in-line connection, but its outlet is positioned near the blood surface.